What a pain, Adobe making me do a bunch of extra work to keep my default settings. Fuck you Adobe.

You can release the source without offering it to be fully licensed. I actually think you might find the closed sales model will result in a lower total income. A model I strongly suggest trying is to offer the code for people to see, help with, etc. Require a license fee (if that’s your idea) for using the software, make the initial license fee very low and be very generous in your trial offering. Ask power users to donate and ask users to donate for feature additions (use a web system for tracking feature requests and allow people to vote by pledging dollars towards new features).

There are tons of email clients out there, most of them have a very small user base or are one of the big ones, you’re trying to compete in a very full field with no clearly best-for-everyone client.

I have spent a lot of time evaluating mail software for every platform and not one has a superset of the best features. I currently use kmail (x11) on OSX, but this is way, way hacky. I love some things about OSX Mail.app, but the closed nature of it and the lack of published API means I can never really feel comfortable in it. It is also missing some features I consider critical: send queue, manual mail filters, arbitrary key assignments…

But every client has its problems. The idea that you’ll be able to pull this off yourself and make it a commercial success out of the blocks while you’re in school seems… ambitious in a “this is never going to happen” sort of way.

Whoever has been telling you closed source = profitable is probably thinking of larger projects. It is my firm belief (and experience) that small projects do better asking for donations and remaining more community-positive. But, either way, good luck. I’m currently having to make some very hard decisions about email clients because not both has the features I want and actually runs well.